Method and apparatus for preparing boron nitride nanotubes by heat treating boron precursor prepared by using air-jet

ABSTRACT

A method and apparatus for preparing boron nitride nanotubes (BNNTs) according to an embodiment may ensure mass-production, may increase yield by reducing a production time, and may prepare BNNTs with high purity. The method includes steps of providing a first powder including boron, forming a second powder including a boron precursor by nano-sizing the first powder, forming a precursor disk by mixing the second powder with a binder; and growing BNNTs on the precursor disk.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No.10-2017-0014753, filed on Feb. 2, 2017, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND Field

One or more embodiments relate to a method and apparatus for preparingboron nitride nanotubes.

Description of the Related Art

Boron nitride nanotubes (BNNTs) have mechanical properties and thermalconductivity that are similar to those of carbon nanotubes (CNTs) thatare generally known. However, CNTs are a combination of conductors andsemiconductors and have low thermal and chemical stability due tooxidation at a temperature equal to or higher than about 400° C.,whereas BNNTs are electrically insulating with a wide band gap of about5 eV and are thermally stable at a high temperature equal to or higherthan about 800° C. in air. Also, boron in BNNTs has thermal neutronabsorption efficiency that is about 200,000 times higher than that ofcarbon in CNTs, and thus has potential to be a radiation-shieldingmaterial.

Technology for mass-producing BNNTs has not been developed yet due todifficulties in a process such as synthesis at a high temperature equalto or higher than 1000° C. Also, it is difficult to increase purity dueto impurities and/or unreacted impurities during preparation of BNNTsand an expensive purification process for removing impurities isrequired.

SUMMARY

One or more embodiments include a method and apparatus for preparingboron nitride nanotubes (BNNTs) that may ensure mass-production and mayincrease yield by reducing a production time.

One or more embodiments include a method and apparatus for preparingBNNTs with high purity.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments.

According to one or more embodiments, a method of preparing boronnitride nanotubes (BNNTs) includes: forming second powder including aboron precursor by nano-sizing first powder including boron; forming aprecursor disk by mixing the second powder with a binder; and growingBNNTs on the precursor disk

The first powder may further include a catalyst.

The nano-sizing of the first powder may include: applying first air to anano-sizing area to form an eddy; applying the first powder to thenano-sizing area; and forming the second powder by using the eddy in thenano-sizing area.

The method may further include collecting the second powder included insecond air including the second powder in the nano-sizing area.

The growing of the BNNTs on the precursor disk may include: locating theprecursor disk in a heating zone of a reaction chamber; heating theheating zone; and applying a reactive gas to the heating zone.

The method may further include: causing a rod to pass through aplurality of the precursor disks; and locating the rod in the heatingzone.

According to one or more embodiments, an apparatus for preparing boronnitride nanotubes (BNNTs) includes: a container including a nano-sizingarea in which first powder is nano-sized to form second powder, a firstinlet through which the first powder is introduced into the nano-sizingarea, a second inlet through which first air is introduced to thenano-sizing area, and an outlet through which second air including thesecond powder is discharged from the nano-sizing area; a first airinjector connected to the second inlet and allowing the first air to beintroduced into the nano-sizing area therethrough; and a collectorconnected to the outlet and including a membrane being enable to passthe second air therethrough and collect the second powder.

The apparatus may further include: a reaction chamber being enable toreceive a precursor disk formed by mixing the second powder with abinder and including at least a heating zone; a rod passing through theprecursor disk; a temperature controller being enable to adjust atemperature of at least the heating zone; a vacuum processor connectedto the reaction chamber and being enable to adjust a degree of vacuum inthe reaction chamber; a gas supply pipe located in the reaction chamberand being enable to apply a reactive gas to at least the heating zone ofthe reaction chamber; and a reactive gas supplier connected to the gassupply pipe and being enable to apply the reactive gas to the gas supplypipe.

The apparatus may further include a cassette configured to receive theprecursor disk and received in the reaction chamber.

The cassette may include: a pair of supports facing each other; a rodlocated between the pair of supports and passing through the precursordisk.

According to one or more embodiments, an apparatus of preparing boronnitride nanotubes (BNNTs) includes: a reaction chamber being enable toreceive a precursor disk formed by mixing powder including a boronprecursor with a binder and including at least a heating zone; a rodpassing through the precursor disk; a vacuum processor connected to thereaction chamber and being enable to adjust a degree of vacuum in thereaction chamber; a gas supply pipe located in the reaction chamber andbeing enable to apply a reactive gas to at least the heating zone of thereaction chamber; and a reactive gas supplier connected to the gassupply pipe and being enable to apply the reactive gas to the gas supplypipe.

The apparatus may further include a cassette configured to receive theprecursor disk and received in the reaction chamber.

The cassette may include: a pair of supports facing each other; and arod located between the pair of supports and passing through theprecursor disk.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1 is a flowchart of a method of preparing boron nitride nanotubes(BNNTs) according to an embodiment;

FIG. 2 is a plan view of a first powder nano-sizing apparatus accordingto an embodiment;

FIG. 3 is a side-sectional view of a collector according to anembodiment;

FIG. 4 is a side-sectional view of a heat treatment apparatus accordingto an embodiment;

FIG. 5 is a partial side-sectional view illustrating a state whereprecursor disks are mounted on a rod according to an embodiment;

FIG. 6 is a partial side-sectional view of the rod according to anembodiment;

FIGS. 7A and 7B are plan views of the precursor disk according toembodiments;

FIG. 8 is a side-sectional view illustrating a part of the heattreatment apparatus according to an embodiment;

FIG. 9 is a side-sectional view of a cassette according to anembodiment;

FIG. 10 is a side-sectional view of the heat treatment apparatusaccording to another embodiment;

FIG. 11A is a scanning electron microscopy (SEM) image illustrating ashape of nano-sized boron nanopowder;

FIG. 11B is a graph showing a result of energy dispersive spectroscopy(EDS) performed on the boron nanopowder;

FIG. 12 is a low-resolution SEM image of a disk plane after a heattreatment process on a precursor disk;

FIG. 13 is a low-resolution SEM image of a disk section after a heattreatment process on a precursor disk;

FIG. 14 is a high-resolution SEM image of a disk section after a heattreatment process on a precursor disk;

FIG. 15 is a transmission electron microscopy (TEM) image of BNNTsprepared by performing a heat treatment process on a precursor disk; and

FIGS. 16A and 16B are respectively an SEM image of prepared BNNTs and agraph showing an EDS result.

DETAILED DESCRIPTION

The present disclosure may include various embodiments andmodifications, and embodiments thereof will be illustrated in thedrawings and will be described herein in detail. The advantages andfeatures of the present disclosure and methods of achieving theadvantages and features will be described more fully with reference tothe accompanying drawings, in which embodiments are shown. The presentdisclosure may, however, be embodied in many different forms and shouldnot be construed as being limited to the embodiments set forth herein.

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings. In the drawings, the sameelements are denoted by the same reference numerals, and a repeatedexplanation thereof will not be given.

It will be understood that although the terms “first”, “second”, etc.may be used herein to describe various elements, these elements shouldnot be limited by these terms. These elements are only used todistinguish one element from another.

As used herein, the singular forms “a”, “an”, and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise.

It will be further understood that the terms “comprises” and/or“comprising” used herein specify the presence of stated features orcomponents, but do not preclude the presence or addition of one or moreother features or components.

Sizes of elements may be exaggerated for convenience of explanation. Inother words, since sizes and thicknesses of elements in the drawings arearbitrarily illustrated for convenience of explanation, the followingembodiments are not limited thereto.

In the following embodiments, the x-axis, the y-axis and the z-axis arenot limited to three axes of the rectangular coordinate system, and maybe interpreted in a broader sense. For example, the x-axis, the y-axis,and the z-axis may be perpendicular to one another, or may representdifferent directions that are not perpendicular to one another.

When a certain embodiment may be implemented differently, a specificprocess order may be different from the described order. For example,two consecutively described processes may be performed substantially atthe same time or performed in an order opposite to the described order.

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items. Expressions such as “atleast one of,” when preceding a list of elements, modify the entire listof elements and do not modify the individual elements of the list.

FIG. 1 is a flowchart of a method of preparing boron nitride nanotubes(BNNTs) according to an embodiment.

Referring to FIG. 1, the method may include nano-sizing first powder S1,forming a precursor disk S2, and growing BNNTs S3.

The nano-sizing of the first powder S1, in which the first powder isnano-sized, may include nano-sizing the first powder and forming secondpowder including a boron precursor.

The first powder may include boron. The boron may be in a powder state.As a mean diameter of boron powder decreases, the quality of preparedBNNTs may increase. The boron powder may have a diameter ranging fromabout 0.01 μm to about 0.5 μm.

The boron may be crystalline and/or amorphous boron.

Since crystalline boron is very hard, the crystalline boron maycontribute to obtaining catalytic metal particles produced from acontainer during nano-sizing, specifically, during a nano-sizing processusing an eddy of air and obtaining seed precursor nanoparticles withhigh efficiency when boron with a nano size is coated on or embedded insurfaces of the catalytic metal nanoparticles. However, when crystallineboron is used, it may take a long time to perform nano-sizing and thusit may take a long time to prepare BNNTs, thereby reducing productivity.Also, when crystalline boron is used, too many catalytic metalnanoparticles may be produced and may act as impurities of finallyprepared BNNTs, thereby increasing impurity contents and reducing thepurity of the BNNTs. Furthermore, an additional sophisticatedpurification process for reducing the impurities is required, therebyincreasing preparation costs.

Accordingly, according to an embodiment, the boron may be amorphousboron, instead of crystalline boron. When amorphous boron is used, boronnanopowder may be obtained even during a short nano-sizing process andBNNTs may be produced in high yield.

The first powder may further comprise a catalyst. The catalyst may beprovided in a powder state. The catalyst is more effective for amorphousboron. That is because when amorphous boron is used, unlike in a casewhere crystalline boron is used in a nano-sizing process using an airjet and/or an eddy of air, catalytic metal nanoparticles may not beproduced and many boron nanoparticles may be prepared in a very shorttime. The catalyst may be combined with boron particles in a process ofnano-sizing the first powder to form precursor nanoparticles, and theprecursor nanoparticles functioning as a seed during preparation ofBNNTs may react with nitrogen to contribute to compounding boron nitride(BN). Catalyst particles may comprise, but are not limited to, iron(Fe), magnesium (Mg), nickel (Ni), chromium (Cr), cobalt (Co), zirconium(Zr), molybdenum (Mo), tungsten (W), and/or titanium (Ti).

A catalytic powder content may range from about 5 wt % to 20 wt % basedon 100 wt % of the boron powder. When the catalytic powder content isless than 5 wt %, sufficient catalyst particles needed to prepare BNNTsmay not be obtained. When the catalytic powder content is greater than20 wt %, boron-catalyst particles in a nano-sizing process using an airjet and/or an eddy of air may not be efficiently combined and thecatalytic powder may act as impurities. When nano-sizing is performedusing the catalytic powder in the above content range, appropriateboron-catalytic nanoparticles may be produced.

According to an embodiment, the nano-sizing of the first powder mayfurther comprise applying first air to a nano-sizing area, applying thefirst powder to the nano-sizing area, and forming the second powder byusing the first air in the nano-sizing area.

FIG. 2 is a plan view of a first powder nano-sizing apparatus 1according to an embodiment.

Referring to FIG. 2, the first powder nano-sizing apparatus 1 accordingto an embodiment may comprise a container 12, a first air injector 14,and a collector 13.

The container 12 may include a nano-sizing area 11, a first inlet 121, asecond inlet 122, and an outlet 123.

The nano-sizing area 11 that is located in the container 12 may be anarea where first powder is nano-sized and second powder is formed. Thenano-sizing area 11 may have a circular shape, as shown in FIG. 2, sothat first air introduced from the second inlet 122 may form an eddy inthe nano-sizing area 11. Although not shown in FIG. 2, the nano-sizingarea 11 may further comprise a structure for more elaborately formingthe eddy.

The first inlet 121 is located at a side surface of the container 12 andcommunicates with the nano-sizing area 11. First powder 101 isintroduced through the first inlet 121 into the nano-sizing area 11. Thefirst inlet 121 may be inclined to form an acute angle with respect to adirection in which the first air flows so that the first powder 101 maybe applied as the first air flows in the nano-sizing area 11.

The second inlet 122 is located at a side surface of the container 12and communicates with the nano-sizing area 11. The first air may beintroduced through the second inlet 122 into the nano-sizing area 11.The second inlet 122 may be inclined with respect to a normal directionof the container 12 so that the first air may become rotational flow inthe nano-sizing area 11.

The second inlet 122 may be connected to the first air injector 14.Although not shown in FIG. 2, the first air injector 14 may comprise acompressed air storage tank and an air pump, and thus the first air thatis a compressed high-speed air jet may be injected into the nano-sizingarea 11.

The outlet 123 may be located at an upper end portion of the container12, and communicates with the nano-sizing area 11. Second air may bedischarged through the outlet 123 from the nano-sizing area 11. Thesecond air refers to a combination of the first air and the secondpowder in the nano-sizing area 11. Although not shown in FIG. 2, theoutlet 123 may further include a gate. The second air may be dischargedto the collector 13 by opening the gate when nano-sizing ends.

According to an embodiment, the first powder may be nano-sized due tothe first air that rotates at a high speed in the nano-sizing area 11.The first powder may be a combination of boron powder and catalyticpowder, as described above. When the boron powder is embedded in anoptimal amount of catalytic powder as nano-sizing is performed in thenano-sizing area 11, an optimal condition and/or particle size for BNNTsynthesis and growth may be provided.

According to a more detailed embodiment, the nano-sizing of the firstpowder may further comprise collecting the second powder included in thesecond air in the nano-sizing area 11.

FIG. 3 is a side-sectional view of the collector 13 according to anembodiment.

The collector 13 may comprise a first collector 131 and a secondcollector 132. According to an embodiment, a plurality of the firstcollectors 131 may be provided, and the number of first collectors 131may be selectively adjusted according to various process conditions suchas air pressure and an amount of the boron.

The first collector 131 may comprise a first membrane 1314 through whichsecond air passes, and the second collector 132 may include a secondmembrane 1324 through which the second air having passed through thefirst membrane 1314 passes and configured to collect second powder 102.

In detail, the first collector 131 may comprise a first bracket 1311located in a first collecting container 1315, a first pipe 1312communicating with the first bracket 1311, the first membrane 1314connected to the first bracket 1311, and a first receiver 1313 coupledto the first bracket 1311.

The first bracket 1311 may be provided to have a vertical pipe shape, asshown in FIG. 3, and may be connected to the first pipe 1312 at at leasta side of the first bracket 1311.

The first pipe 1312 is connected to the outlet 123 and receives thesecond air 103.

The first membrane 1314 may be coupled to an end, for example, an upperend portion, of the first bracket 1311 and may filter the second powder102 when the second air 103 passes through the first membrane 1314. Anair pore size or a density of the first membrane 1314 may be determinedbased on a desired boron particle size.

The first receiver 1313 may be coupled to the other end, for example, alower end portion, of the first bracket 1311 and may receive powderfiltered by the first membrane 1314. Although not shown in FIG. 3, afilter and/or a mesh may be further provided between the first receiver1313 and the first bracket 1311 to prevent the powder received in thefirst receiver 1313 from entering back to the first membrane 1314.

Accordingly, the second air 103 ejected from the outlet 123 flowsthrough the first pipe 1312 to the first membrane 1314, and powder 104filtered by the first membrane 1314 is received in the first receiver1313. The second air 103 having passed through the first membrane 1314is received in the first collecting container 1315.

As a plurality of the first collectors 131 are connected to one another,the first pipe 1312 of one first collector 131 communicates with thefirst collecting container 1315 of the first collector 131 at a moreupstream position, and thus powder of the second air 103 is sequentiallyfiltered. Accordingly, the powder 104 received in the first receiver1313 at a upstream position has a larger diameter than that received inthe first receiver 1313 at a downstream position, and the second powder102 is sequentially filtered toward a more downstream position.

The second collector 132 may be located at a lowermost downstreamposition of the collector 13.

The second collector 132 may comprise a second bracket 1321, a secondpipe 1322 communicating with the second bracket 1321, the secondmembrane 1324 connected to the second bracket 1321, and a secondreceiver 1323 coupled to the second bracket 1321.

The second bracket 1321 may be provided to have a vertical pipe shape,as shown in FIG. 3, and may be connected to the second pipe 1322 at atleast a side of the second bracket 1321.

The second pipe 1322 receives the second air 103 from the firstcollector 131 adjacent to the second pipe 1322.

The second membrane 1324 may be coupled to an end, for example, an upperend portion, of the second bracket 1321 and may filter the second powder102 as the second air 103 passes through the second membrane 1324. Anair pore size and a porosity of the second membrane 1324 may bedetermined based on a desired boron particle size.

The second receiver 1323 may be coupled to the other end, for example, alower end portion, of the second bracket 1321 and may receive the secondpowder 102 filtered by the second membrane 1324. Although not shown inFIG. 3, a filter and/or a mesh may be further provided between thesecond receiver 1323 and the second bracket 1321 to prevent powderreceived in the second receiver 1323 from entering back to the secondmembrane 1324.

Although the second collector 132 does not include a collectingcontainer in FIG. 3, the present disclosure is not limited thereto.According to another embodiment, the second bracket 1321, the secondmembrane 1324, and the second receiver 1323 may be received in acollecting container, and air received in the collecting container maybe discharged by an additional ejector.

Accordingly, the second powder 102 in the second air 103 may be filteredby sequentially passing through the first collector 131 and the secondcollector 132, and the second powder 102 with the smallest diameter maybe received in the second receiver 1323 that is located at a lastposition.

The first membrane 1314 and/or the second membrane 1324 may be replaced,for example, with membranes having a pore size and a porosity suitableto obtain the second powder 102 with a desired diameter.

The second powder 102 may comprise catalyst particles with a largediameter that are not nano-sized in a nano-sizing process and/or are notfiltered in a collecting process.

The catalyst particles with a large diameter may act as impurities offinally obtained BNNTs, thereby reducing purity. It is preferable toremove particles with a diameter greater than 1,000 nm. Accordingly, apurification process of removing catalyst particles with a largediameter may be performed.

In the purification process, nanopowder formed by an air jet and/or aneddy may be dispersed in a solvent, catalytic powder with a largediameter in a dispersed solution may be separated by using a magnet, andhigh purity boron-based nano precursor powder from which catalystparticles with a large diameter are removed may be obtained bycollecting and drying a supernatant of the dispersed solution.

The purification process may be performed using a centrifugal force,instead of the magnet. For example, catalytic powder with a largediameter may be removed at 500 to 2,000 rpm by using a centrifugalseparator.

The purification process may be performed at low costs, and does notincrease process costs. In this case, although the solvent is notlimited, it is preferable that the solvent does not act as impuritiesduring preparation of BNNTs. Accordingly, it is preferable that thesolvent is easily removed after the purification process, and preferableexamples of the solvent may comprise ethanol and water. It is morepreferable that ethanol is used as the solvent by taking into accountefficiency in drying a supernatant.

In forming of the precursor disk S2, the collected second powder may beshaped into a precursor disk. Since the second powder is shaped into aprecursor disk and undergoes a reaction process, reaction yield may beincreased and mass-production may be ensured.

To this end, the precursor disk may be formed by mixing a binder thatdoes not act as impurities during preparation of BNNTs with the secondpowder that is precursor powder to obtain a mixture and heating and/orpressing the mixture at an appropriate temperature.

The precursor disk may be prepared according to a method of anembodiment, and BNNTs may be prepared by heat treating the precursordisk. Accordingly, the precursor disk does not have to have a highcombination force or high shape stability as long as the precursor diskmay maintain a shape thereof at a temperature and pressure in a reactionchamber.

The binder may comprise sucrose, treacle, grain syrup, polypropylenecarbonate (PPC), a vinyl-based material such as polyvinyl alcohol (PVA)or polyvinyl butyral (PVB), and a cellulose-based material such as ethylcellulose (EC). Since the binder vaporizes and is removed in ahigh-temperature heat treatment process of firing and nitriding thesecond powder that is precursor powder, the binder does not remain inBNNTs and does not act as impurities.

A binder content may range from about 5 wt % to about 50 wt % based on100 wt % of the precursor powder. When the binder content is less than 5wt %, it may not be easy to shape powder into a disk and it may bedifficult to maintain a shape of the precursor disk. When the bindercontent is greater than 50 wt %, pores are formed in a film after abinder component vaporizes and is removed. In this case, too many poresmay reduce the reliability of the precursor disk.

The precursor disk may be formed on a separative film, for example, arelease film. For example, a release film may be inserted into a mold,mixed powder of precursor powder and binder powder may be uniformlydistributed on the release film, and the precursor disk having apredetermined shape may be prepared by pressing the mixed powder.Preferably, the release film may be removed and then the precursor diskmay be put in a heat treatment chamber.

In this case, the binder may be used in a powder state or a liquidstate.

Any binder that may be used in a powder state from among components thatmay be appropriately used as the binder may be appropriately used in thepresent disclosure as long as the binder has a solid state at roomtemperature. Examples of the binder that may be used in a powder statemay comprise sucrose, treacle, grain syrup, PPC, a vinyl-based materialsuch as PVA or PVB, a cellulose-based material such as EC, and a resinsuch as epoxy.

When the binder is used in a powder state, in order to form theprecursor disk, the precursor powder and binder powder is mixed toobtain mixed powder, the mixed powder is uniformly distributed and thenis pressed at an appropriate temperature to prepare the precursor disk.In detail, the precursor disk may be prepared by uniformly distributingthe mixed powder in a mold in which the mixed powder may be shaped intoa predetermine disk, pressing the mixed powder by using a hot pressingprocess at a predetermined temperature to increase a viscosity of thebinder powder, and inducing adhesion of the precursor powder.

In this case, a temperature of the hot pressing process may range fromabout 50° C. to about 150° C. When the temperature is lower than 50° C.,adhesion due to a viscosity of the binder powder may not be ensured, andwhen the temperature is higher than 150° C., the binder powder may meltor vaporize and thus it may not be easy to release a film or performshaping.

When the binder is used in a liquid state, a disk may be simply formedby mixing the precursor powder with a liquid binder to obtain a mixture,uniformly distributing the mixture on a release film, applying heat to apredetermined temperature, and pressing and drying the mixture.

In this case, the liquid binder may be obtained by applying water to abinder such as sucrose, treacle, grain syrup, or PVA.

The liquid binder may be obtained by applying a solvent to a binder suchas PPC, PVB, or EC. In this case, the solvent may be appropriatelyselected according to a type of a binder. Ketone or ethyl acetate may beused for PPC, methanol or ethanol may be used for PVB, and terpinol maybe used for EC.

Alternatively, the precursor disk may be formed by distributing amixture of the precursor powder and a binder on a predeterminedsubstrate and then pressuring and/or heating the mixture, and thesubstrate on which the precursor disk is formed may be put in a reactionchamber. In this case, the precursor disk may be formed on a surface orboth surfaces of the substrate. The precursor disk may be formed byapplying the mixture on the substrate in the same manner as thatdescribed for a case where a disk is formed on a release film.

In this case, it is preferable that the substrate is formed of amaterial that may withstand heat treatment at a high temperature becausethe substrate may be located in a heat treatment chamber. Accordingly,the substrate may be formed of, for example, a metal such as stainlesssteel (STS), tungsten (W), or titanium (Ti), or ceramic such as siliconcarbide or alumina.

It is preferable that the precursor disk is thin by taking into accountreaction efficiency with nitrogen in a reaction chamber. However, it ispreferable that the precursor disk is thick by taking into account shapestability for maintaining a shape of the precursor disk in the reactionchamber. In particular, a binder used in preparation of the precursordisk vaporizes in a heat treatment process, and thus pores are formed inthe precursor disk during the heat treatment.

For example, when sucrose is used as a binder, a thermal decompositionprocess may be defined by using the following chemical formula.C₁₂H₂₂O₁₁ (Sucrose)+heat→3CO₂+5H₂O+6H₂

The pores may affect shape stability of the precursor disk, therebydeforming the precursor disk. Accordingly, the precursor disk may have athickness that is equal to or greater than 100 μm.

When a thickness of the precursor disk is too large, reaction efficiencymay be reduced to the large thickness. However, since a transmittance ofa reactive gas may be increased due to pores formed during vaporizationof a binder component, BNNT preparation yield may be improved. As aresult, a decrease in reaction efficiency due to a large thickness maybe offset by pores. However, a thickness of the precursor disk may notexceed 1,000 μm.

In growing of the BNNTs S3, BNNTs are grown by heat treating theprecursor disk.

The BNNTs may be grown by locating the precursor disk in a heating zoneof a reaction chamber, heating the heating zone, and applying a reactivegas to the heating zone.

In this case, the precursor disk may be located in the reaction chamberso that the reactive gas may contact the precursor disk as much aspossible. For example, the precursor disk may be vertically located in areaction chamber with a horizontal cylindrical shape, that is, in adirection perpendicular to a bottom surface of the horizontalcylindrical reaction chamber. Since the precursor disk is verticallylocated, a plurality of the precursor disks may be located in thereaction chamber, thereby mass-producing BNNTs by using one heattreatment process. Also, since the precursor is formed as a thin film, anitrogen-containing reactive gas may contact both surfaces of theprecursor disk, thereby increasing a reaction area and increasing BNNTproduction yield.

A vertical arrangement of the precursor disk in the reaction chamberwith the horizontal cylindrical shape is not limited, and may beappropriately selected by taking into account an inner shape of thereaction chamber, that is, reaction efficiency and efficiency in the useof an inner surface of the reaction chamber.

The reaction chamber is not limited as long as the reaction chamber isused to synthesize BNNTs. However, the reaction chamber may include adevice for aligning the precursor disks.

Also, a nitrogen-containing reactive gas may be applied into thereaction chamber to prepare BNNTs from the precursor disk located in thereaction chamber. In this case, the reaction chamber may include areactive gas distributor in order to distribute the nitrogen-containingreactive gas. The reactive gas distributor may apply the reactive gas tothe precursor disk in a direction perpendicular or parallel to theprecursor disk.

Although the reactive gas applied to the reaction chamber is notlimited, nitrogen (N₂) or ammonia (NH₃) may be applied or a mixed gas ofN₂ and NH₃ may be applied to the reaction chamber. Alternatively, amixed gas of N₂, NH₃, and hydrogen (H₂) may be used.

The reactive gas may be applied to the reaction chamber at a speedranging from about 20 sccm to about 500 sccm. When the reactive gas isapplied at a speed less than 20 sccm, nitriding efficiency of boron maybe reduced due to insufficient supply of nitrogen, and thus a reactionmay need to be performed for a long time. When the reactive gas isapplied at a speed greater than 500 sccm, boron powder in the precursordisk in a solid state may be ablated due to a high speed of the reactivegas, and thus BNNT production yield may be reduced.

BNNTs may be obtained by performing a heat treatment in the reactionchamber at a pressure equal to or less than 2 atm and a temperatureranging from about 1,100° C. to about 1,300° C. for 2 to 6 hours.

According to an embodiment, a heat treatment apparatus 3 of FIG. 4 maybe provided.

According to an embodiment, the heat treatment apparatus 3 may comprisea reaction chamber 31, a temperature controller 39, a vacuum processor32, a gas supply pipe 33, and a gas supplier 34.

The reaction chamber 31, in which a precursor disk is received, mayinclude a heating zone where an appropriate temperature for a reactionmay be maintained. The reaction chamber 31 may include, but is notlimited to, an alumina pipe, and may be formed of a heat-resistantmaterial that may withstand a temperature of up to about 1,500° C.

A loading chamber 321 and an unloading chamber 322 may be respectivelyconnected to a front end and a rear end of the reaction chamber 31, andgates 323 may be respectively provided between the reaction chamber 31and the loading chamber 321 and between the reaction chamber 31 and theunloading chamber 322 to separate an environment in the reaction chamber31.

The vacuum processor 32 may be connected to the reaction chamber 31 andmay adjust a degree of vacuum in the reaction chamber 31. To this end,the vacuum processor 32 may comprise a vacuum pump and a controller.Although the vacuum processor 32 is connected to the loading chamber 321in FIG. 4, the present disclosure is not limited thereto and the vacuumprocessor 32 may be connected to the unloading chamber 322.

The temperature controller 39 may be connected to the reaction chamber31. Although not shown in FIG. 4, the temperature controller 39 maycomprise a heater that directly adjusts a temperature in the reactionchamber 31 and a controller that controls the heater.

The gas supply pipe 33 may extend in the reaction chamber 31, and areactive gas may be applied through the gas supply pipe 33 to at leastthe heating zone of the reaction chamber 31. Accordingly, the gas supplypipe 33 may have a length greater than that of the heating zone and maybe provided to pass through the heating zone of the reaction chamber 31.A plurality of gas discharge holes may be formed in the gas supply pipe33 so that a gas may be supplied through the gas supply pipe 33 into thereaction chamber 31.

The gas supply pipe 33 may extend along the reaction chamber 31.

The gas supply pipe 33 may be connected to the gas supplier 34 locatedoutside the reaction chamber 31, and although not shown in FIG. 4, thegas supplier 34 may comprise a reactive gas storage tank and a gassupply pump.

According to an embodiment, a gas discharge pipe 35 may extend into thereaction chamber 31. The gas discharge pipe 35 may be located outside atleast the heating zone of the reaction chamber 31. Accordingly, areactive gas for which a reaction has been completed may be dischargedto the outside of the reaction chamber 31 and pressure in the reactionchamber 31 may be prevented from excessively increasing.

The gas discharge pipe 35 may be connected to a gas discharge unit 36located outside the reaction chamber 31, and although not shown in FIG.4, the gas discharge unit 36 may comprise a valve for adjusting pressurein the reaction chamber 31 and a gas discharge pump.

The precursor disk may be located in the reaction chamber 31. Accordingto an embodiment, as shown in FIG. 5, a rod 37 may pass through aplurality of precursor disks 2, and the rod 37 may be located in atleast the heating zone of the reaction chamber 31. The rod 37 may belocated in a direction parallel to a longitudinal direction of thereaction chamber 31.

As such, according to an embodiment, BNNTs may be simultaneouslysynthesized and grown by allowing the rod 37 to pass through theplurality of precursor disks 2. Accordingly, since the whole reactionspace in the reaction chamber 31 may be used, productivity and/or yieldmay be maximized.

The precursor disks 2 may be located on the rod 37 at predeterminedintervals. The number of precursor disks 2 introduced into the reactionchamber 31 may be adjusted by adjusting an interval between theprecursor disks 2.

A plurality of notches 371 may be formed in the rod 37 so that theprecursor disks 2 are fixed to the rod 37 through the notches 371.Accordingly, an interval between the precursor disks 2 and/or the numberof precursor disks 2 may be adjusted by adjusting an interval betweenthe notches 371.

The precursor disk 2 may be formed to correspond to a shape of an innerspace of the reaction chamber 31. When the inner space of the reactionchamber 31 has a circular shape, a disk body 21 with a circular shapemay be provided as shown in FIG. 7A. A loading hole 22 may be formed ata central portion of the disk body 21 and the rod 37 may pass throughthe loading hole 22.

A diameter of the disk body 21 of the precursor disk 2 may be less thanan inner diameter of the reaction chamber 31.

A precursor disk 2′ according to another embodiment illustrated in FIG.7B may further include a groove 23 formed in an edge portion of the diskbody 21. When the gas supply pipe 33 is formed on a side of the reactionchamber 31, the disk body 21 may not interfere with the gas supply pipe33 due to the groove 23.

A heating zone 311 may be located at a substantially central portion ofthe reaction chamber 31, as shown in FIG. 8, and a length of the heatingzone 311 may be adjusted according to a capacity of the temperaturecontroller 39 of the reaction chamber 31.

According to an embodiment, the supplying density of a reactive gas 331supplied to the heating zone 311 may vary. That is, a large amount ofreactive gas 331 may be applied to a middle portion of the heating zone311 where a reaction most actively occurs and a smaller amount ofreactive gas 331 may be applied to portions other than the middleportion.

In this structure, BNNTs may be prepared in a continuous process asdescribed below.

According to an embodiment, to this end, as shown in FIG. 9, theprecursor disks 2 may be received in a cassette 38, and as shown in FIG.10, the precursor disks 2 may be continuously applied to the reactionchamber 31.

The reaction cassette 38 may comprise a pair of supports 381 facing eachother and the rod 37 may be coupled between the supports 381. Thesupports 381 and the rod 37 may be detachably provided, and theprecursor disks 2 may be arranged on the rod 37 as described above. Thesupports 381 may be formed of, but are not limited to, alumina that is aheat-resistant material.

Although not shown in FIG. 9, at least one hole may be formed in each ofthe supports 381. The hole may prevent pressure of a reactive gas in thereaction cassette 38 from being excessively maintained by the supports381 and may appropriately maintain pressure of a reactive gas in thereaction chamber 31. The holes of the supports 381 may be symmetric witheach other so that a reactive gas smoothly and uniformly flows in bothdirections.

The cassettes 38 may be continuously introduced into the reactionchamber 31, as shown in FIG. 10.

First, a temperature and a gas atmosphere in the reaction chamber 31 areoptimized, and the cassette 38, in which the precursor disks 2 arereceived, is introduced through the loading chamber 321 into thereaction chamber 31. In this case, since the gate 323 is located betweenthe loading chamber 321 and the reaction chamber 31, an atmosphere inthe reaction chamber 31 may be maintained to the maximum and thecassette 38 may be received in the reaction chamber 31.

Although not shown in FIG. 10, an additional transfer device fortransferring the cassette 38 to the reaction chamber 31, an auxiliarygate, and a vacuum pump may be provided in the loading chamber 321. Inthis case, when the gate 323 of the reaction chamber 31 is opened, thereaction chamber 31 and the loading chamber 321 operate at the samereactive atmosphere and the same pressure, the cassette 38 istransferred from the loading chamber 321 to the reaction chamber 31, andthen the gate 323 is closed.

When the gate 323 is closed, the auxiliary gate of the loading chamber321 is opened, a new cassette 38 is introduced, the auxiliary gate isclosed, and the new cassette 338 is transferred to the reaction chamber31 as described above. During this operation, the loading chamber 321prevents the precursor disks 2 of the cassette 38 from beingcontaminated by using the auxiliary gate and the vacuum pump and makesan atmosphere in the loading chamber 321 similar to that in the reactionchamber 31.

The cassettes 38 may be sequentially transferred toward the unloadingchamber 322 in the above manner and may be horizontally stacked in thereaction chamber 31.

Next, when the gate 323 is opened, the cassette 38 may be moved to theunloading chamber 322, and when the gate 323 is closed, the cassette 38may be ejected from the unloading chamber 322.

In this process, the amount of a reactive gas that is supplied may beadjusted as shown in FIG. 9 so that a reaction with the reactive gas maymost actively occur when the cassette 38 is located at a central portionof the heating zone 311.

When BNNTs are grown by heat treating powder by using a generally knownmethod, processes of increasing a temperature, maintaining thetemperature, synthesizing BNs, growing BNNTs, decreasing a temperature,cooling at room temperature, and removing a reactant have to beperformed, there is a limitation in volume of one time production ofBNNTs, and cost increases due to increase in required energy and time.

However, according to an embodiment, since BNNTs are continuouslyprepared in an in-line manner by using the above method, BNNTpreparation yield and productivity may be maximized.

A method of preparing BNNTs according to an embodiment will now beexplained in more detail. However, the present disclosure is not limitedthereto.

In order to prepare a nano boron precursor for BNNT synthesis, amorphousboron powder that had a magnesium (Mg) impurity content of about 3.5 wt% and a mean diameter of 5 μm and iron (Fe) powder that was a metalcatalyst and had a mean diameter of about 50 nm were mixed together toform first powder. The first powder comprised 4 g of amorphous boron and0.4 g of iron (Fe). Next, an operation may be performed for 5 minuteswith first air accelerated by using, for example, the first powdernano-sizing apparatus 1 of FIG. 2, to prepare boron precursornanopowder, that is, second powder.

6 g of nano-sized and collected boron precursor nano powder and 4 g offinely grinded sucrose were uniformly mixed together to form a mixture,and the mixture was applied by using a mesh having fine pores to beuniformly distributed between a donut-shaped mold with a thickness of150 μm and a release film and then was pressed by using a hot pressingprocess at 150° C. to prepare a disk with a thickness of 150 μm.

Donut-shaped precursor disks shaped as shown in FIG. 7A were loaded on arod and put in a heat treatment chamber, as shown in FIG. 5.

Next, a mixed gas of N₂ (90 vol %) and NH₃ (10 vol %) was heat treatedat a flow rate of 200 sccm at 1,200° C. for 4 hours to obtain BNNTs.

FIG. 11A is a scanning electron microscopy (SEM) image illustrating ashape of nano-sized boron nanopowder. Boron particles with a nano sizediameter were dispersed in agglomerates. FIG. 11B is a graph showing aresult of energy dispersive spectroscopy (EDS) performed on aquadrangular portion (see FIG. 11A) of the boron nanopowder obtainedthrough the nano-sizing process. A boron (B) content was about 83.01 wt%, an iron (Fe) content was about 5.51 wt %, a magnesium (Mg) contentwas about 3.39 wt %, an oxygen (0) content was about 4.91 wt %, and aplatinum (Pt) content was about 3.11 wt %. Mg that already existed asimpurities in amorphous boron powder and may perform as a catalyst likeFe was dispersed in an appropriate amount. It is found from FIG. 11Bthat catalytic metal nanoparticles were embedded in the boronnanoparticles prepared by using a nano-sizing process using an eddy ofair of the present disclosure to obtain an efficient seed for synthesisand growth of nanotubes.

FIG. 12 is a low-resolution SEM image of a disk plane after a heattreatment process on a precursor disk. A binder was removed from theprecursor disk and a sufficient number of pores were formed.Accordingly, a reactive gas may pass through the entire precursor diskand a reaction may efficiently occur.

FIG. 13 is a low-resolution SEM image of a disk section after a heattreatment process on a precursor disk. Referring to FIG. 13, BNNTs weregrown in the precursor disk to a thickness of about 150 μm.

FIG. 14 is a high-resolution SEM image of a disk section after a heattreatment process on a precursor disk. Referring to FIG. 14, BNNTs weregrown in the precursor disk. As described above, pores may be formed inthe precursor disk when a binder included in the precursor diskdisassociated and/or evaporated, and thus a reactive gas may passthrough the precursor disk.

FIG. 15 is a transmission electron microscopy (TEM) image of BNNTsprepared by performing a heat treatment process on a precursor disk.Referring to FIG. 15, nanotubes with a mean diameter of 50 nm or lesswere grown straight and long.

FIGS. 16A and 16B are respectively an SEM image of prepared BNNTs and agraph showing an EDS result. As shown in FIG. 16B, BNNTs of which theratio between nitrogen and boron was about 1:1 were formed and had adegree of purity of about 97.5%.

A method and apparatus for preparing BNNTs according to the one or moreembodiments may ensure mass-production, may increase yield by reducing aproduction time, and may prepare BNNTs with high purity.

While the present disclosure has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby one of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present disclosure as defined by the following claims.

The particular implementations shown and described herein areillustrative examples of the present disclosure and are not intended tootherwise limit the scope of the present disclosure in any way. For thesake of brevity, conventional electronics, control systems, softwaredevelopment, and other functional aspects of the systems may not bedescribed in detail. Furthermore, connecting lines, or connectors shownin the various figures presented are intended to represent exemplaryfunctional relationships and/or physical or logical couplings betweenthe various elements. It should be noted that many alternative oradditional functional relationships, physical connections or logicalconnections may be present in a practical device. Moreover, no item orcomponent is essential to the practice of the present disclosure unlessthe element is specifically described as “essential” or “critical”.

The use of the terms “a” and “an”, and “the” and similar referents inthe context of describing the present disclosure (especially in thecontext of the following claims) are to be construed to cover both thesingular and the plural. Furthermore, recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. Also, thesteps of all methods described herein can be performed in any suitableorder unless otherwise indicated herein or otherwise clearlycontradicted by context. The present disclosure is not limited to thedescribed order of the steps. The use of any and all examples, orexemplary language (e.g., “such as”) provided herein, is intended merelyto better illuminate the present disclosure and does not pose alimitation on the scope of the present disclosure unless otherwiseclaimed. Numerous modifications and adaptations will be readily apparentto one of ordinary skill in the art without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A method of preparing boron nitride nanotubes(BNNTs), the method comprising steps of: providing a first powder bymixing boron and a catalyst powder; forming a second powder comprising aboron precursor by nano-sizing the first powder; forming a precursordisk having a thickness of 100 μm to 1000 μm by mixing 100 wt % of aprecursor powder with 5 to 50 wt % of a binder including at least one ofsugar, syrup, grain syrup, polypropylene carbonate, polyvinyl alcohol,polyvinyl butyral, and ethylcellulose; and growing BNNTs on theprecursor disk; wherein the growing of the BNNTs on the precursor diskcomprises steps of: locating the precursor disk in a heating zone of areaction chamber; heating the heating zone; and applying a reactive gasto the heating zone to thereby grow the BNNTs by forming pores on theprecursor disk as the binder is sublimated and removed; and wherein thenano-sizing of the first powder comprises steps of: applying first airin a direction inclined to a perpendicular direction of a roundnano-sizing area; applying the first powder to the nano-sizing area toform an acute angle towards a flow direction of the first air; andforming the second powder by using the first air in the nano-sizingarea.
 2. The method of claim 1, further comprising a step of: collectingthe second powder in a second air in the nano-sizing area.
 3. The methodof claim 2, wherein the step of collecting the second powder comprisessteps of: causing the second air to pass through a first membraneconnected to the nano-sizing area; causing the second air to becollected to a first collecting container for accommodating the firstmembrane; causing the second air from the first collecting container topass through a second membrane; and accommodating the second powder in areceiver connected to the second membrane.
 4. The method of claim 1,further comprising steps of: causing a rod to pass through a pluralityof the precursor disks; and locating the rod in the heating zone.
 5. Themethod of claim 4, further comprising steps of: causing a cassettehaving a plurality of the rods to be positioned within a reactionchamber, wherein a reaction gas is supplied from a lower part of thecassette.